Running scripts in Bash Scripting - Step-by-Step Execution

Concept Flow - Running scripts

Write script file

↓

Make script executable

↓

Run script with ./ or bash

↓

Script runs commands

↓

Output shown in terminal

↓

Script ends

This flow shows how you write a script, make it executable, run it, and see the output in the terminal.

Execution Sample

Bash Scripting

#!/bin/bash
 echo "Hello, world!"

This script prints 'Hello, world!' when run.

Execution Table

Step	Action	Command/Code	Result/Output
1	Create script file	echo -e '#!/bin/bash\n echo "Hello, world!"' > hello.sh	File 'hello.sh' created with script content
2	Make script executable	chmod +x hello.sh	Script 'hello.sh' is now executable
3	Run script	./hello.sh	Hello, world!
4	Script ends	Script finishes running	Terminal prompt returns

💡 Script finishes after printing output and terminal prompt returns

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
hello.sh file	Does not exist	Created with script content	Exists and executable	Executed and output shown	Exists and executable

Key Moments - 3 Insights

Why do we need to make the script executable before running it?

The script must have execute permission to run with './'. Without it, the system will refuse to run the file. See execution_table step 2 and 3.

Can we run the script without making it executable?

Yes, by running 'bash hello.sh' you don't need execute permission. This runs the script with the bash interpreter directly. See execution_table step 3 alternative.

What does the '#!/bin/bash' line do?

It tells the system to use bash to run the script. This is called a shebang. Without it, the system might use a different shell.

Visual Quiz - 3 Questions

Look at the execution table, what is the output when running the script at step 3?

A Hello, world!

B Script not found

C Permission denied

D No output

💡 Hint

Check the 'Result/Output' column at step 3 in the execution_table

At which step is the script made executable?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column in the execution_table for making executable

If we skip step 2 and try to run './hello.sh', what will likely happen?

A Script runs normally

B Permission denied error

C File not found error

D Script prints nothing

💡 Hint

Refer to key_moments about execute permission and step 2 in execution_table

Concept Snapshot

Running scripts in bash:
1. Write your script in a file (e.g., hello.sh).
2. Make it executable with 'chmod +x filename'.
3. Run it with './filename' or 'bash filename'.
4. The script runs commands and shows output.
5. The shebang '#!/bin/bash' tells which shell to use.

Full Transcript

To run a bash script, first create a file with your commands. For example, a file named hello.sh with the content '#!/bin/bash' and 'echo "Hello, world!"'. Next, make the script executable using 'chmod +x hello.sh'. This allows you to run it directly with './hello.sh'. When you run it, the script executes the commands inside and prints 'Hello, world!' to the terminal. The script ends and the terminal prompt returns. Alternatively, you can run the script without making it executable by using 'bash hello.sh'. The first line '#!/bin/bash' tells the system to use bash to run the script. Without execute permission, running './hello.sh' will give a permission denied error.